Willian Jose and Fornals on debut were the goalscorers for the 2-0 win.
Former West Ham midfielder Fornals said: "My first start, very grateful for the opportunity, to my teammates and to everyone for the goal. The game has been very complete from the first minute. From here I congratulate Cádiz, that they can fight until the end and that they do as well as possible.
"When you look to come to a team like Betis, you are afraid of how to fit in because it is full of great players, but it is easier for them to make you shine. Very grateful for the week I came working with them and to continue working to give joy.
"We drew the previous day, these three points, now to think about Europe and come back stronger for the next one. Anything that means thinking beyond that would be a mistake when we have five very beautiful months ahead of us."